The present disclosure relates to methods, systems and apparatus for deriving an indication of a communications parameter at communications devices in a wireless communications system.
As network entities such as eNodeBs in wireless telecommunications systems are required to provide an increasing number of network functionalities, it becomes more important for each network entity to be able to indicate at least some of those functionalities at an appropriate point in the network signalling process. It is expected that network entities of differing network functionality capabilities will be deployed alongside one another in many wireless communications networks: as a result, a telecommunications device (i.e. a user equipment, UE) wishing to access a particular network capability cannot presume that any given network entity from which it requests such a service can actually deliver the service, and where the capability is absent, the UE must start over requesting the capability from a different network entity, incurring a penalty in terms of wasted time and processing power.
Certain classes of telecommunications device, such as MTC devices (e.g. semi-autonomous or autonomous wireless communication terminals), support “low capability” communication applications that are characterised, for instance, by the transmission of small amounts of data at relatively infrequent intervals. MTC devices are constructed so that individually they represent little burden on telecommunications networks and thus can be deployed in greater numbers than equivalent “full capability” terminals in the same networks.
To support MTC terminals, it has been proposed to introduce a “virtual carrier” operating within a bandwidth of one or more “host carriers”: the proposed virtual carrier concept preferably integrates within the transmission resources of conventional OFDM based radio access technologies and subdivides frequency spectrum in a similar manner to OFDM. Unlike data transmitted on a conventional OFDM type downlink carrier, data transmitted on the virtual carrier can be received and decoded without needing to process the full bandwidth of the downlink OFDM host carrier.
The virtual carrier concept is described in a number of co-pending patent applications (including GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9]), the contents of which are incorporated herein by reference.
“Virtual carrier” operation needs to be supported by a suitable “VC” functionality in the cell (i.e. provided by the serving network entity). Thus the initial procedures for a UE to access a cell could waste processing effort if a cell does not in fact support the VC. An MTC device is typically designed to operate with low power and long battery life, and it is therefore especially desirable to minimise such wasted effort in this case.
In current systems, the initial procedures are largely designed with the assumption that the UE certainly wishes to connect to the cell (unless it is barred in some way, by virtue of the public land mobile network operator (PLMN) identity, for example), but this may not be true for a UE with restricted capability. Particularly in MTC scenarios, there is the possibility of an event occurring that triggers many MTC UEs to try to connect with the network. This could overload the network and so it may be desirable to indicate to UEs that they should not even try to connect in order to save transmit power and processing power at the eNB and to reduce potentially significant interference.
The conventional initial procedure for cell acquisition does not currently have any facility for efficiently indicating such capabilities (or ability to offer such functionality).
An efficient communication of network entity capability within a wireless telecommunications system is therefore desirable.